NanoGear: An Interlocking Mechanical System in the Molecular Scale

Gears and transmission systems are among the most widely used mechanical systems today, and a new study could take its basic concepts down to the molecular level.

The Emilia-Romagna region in the northern part of Italy is known as "the Motor Valley." A research team from the University of Bologna together with the Institute for Organic Synthesis and Photoreactivity of the National Research Council (Cnr-Isof), both located at the heart of the Italian region, has designed, constructed, and successfully operated NanoGear: a mechanical system in the molecular scale. It is composed of interlocking molecular components and designed to work like the conventional gear system.

Working on the molecular scale, in the range of nanometers, the NanoGear is an extremely small device and is the tiniest gear ever produced in Italy's Motor Valley.

Designing and Fabricating the NanoGear

"The transmission and transformation of nanometric movements in biological molecules are the basis of the main functions of living organisms. Nevertheless, these phenomena are poorly understood in artificial molecules because they are extremely difficult to identify and observe," explains Alberto Credi, a co-author of the study from the Department of Industrial Chemistry "Toso Montanari" at the University of Bologna and the Center for Light Activated Nanostructures of the ISOF-CNR, in the university news release.

Credi additionally explains: "The construction of molecular devices such as NanoGear is a first step forward towards the development of ultra-miniaturized mechanical devices based on molecular motors, with potential breakthrough applications in various fields of technology and medicine."

The NanoGear mechanical system is a molecular structure belonging to the molecular class of rotaxanes. It has three components: a ring that slides along an axle that has a rotor attached in its center.

The ring can move along the length of the axle but is stopped at both ends by two bulky molecular groups. Meanwhile, the rotor at the middle can rotate along its own axis and is supported by two different "blades" that allow for the observation of its movement.

In the new mechanical system in the molecular scale, its main design element is the presence of the rotor being directly connected to the axis through a covalent bond. On the other hand, the stoppers keep the ring along the length of the axis. As for its rates of movement, both the rotor and the ring depend on the thermal energy present in the NanoGear. Since it is not connected to any form of "motor," the NanoGear is essentially running in "neutral."

Observing the NanoGear in Motion

Researchers used nuclear magnetic resonance techniques to observe the mechanical system's response and to measure its rates as reported in the article "Stereodynamics of E/Z isomerization in rotaxanes through mechanical shuttling and covalent bond rotation," appearing in the latest Chem journal.

They then observed that at 65°C, the ring starts shuttling along the length of the axle at about 7 times per minute, passing over the rotor as it does. In the same period, the rotor spins about 260 times - showing that the two NanoGear motions are not synchronous with each other. However, they mutually influence the response of each other.

Another unexpected and important result is the effect created by the medium in which the new molecule is dispersed. Researchers discovered that by changing the solvent material, one movement slows down while the other speeds up. This behavior, however, has no direct equivalent in the macroscopic world, making this nanoscale lubricating behavior potentially useful for radical innovations in the future.

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